Cisco VTP (Virtual Truking Protocol) Tutorial With Examples

This is my first post about my CCNP journey. I have all ready pass Routing exam. Now I am working on Switching. So my post would be about Switching for a period of time. To day I will write about VTP protocol. There is a lot of articles about VTP but I want to describe it from my point of view to understand it better.

VTP (Virtual Trunking Protocol) is used to manage vlan info (addition,deletion, …) between switches that reside in an area. It workes on layer 2. If correctly configured managing vlans in the domain is very easy. Domain is a collecion of switches that is configured with the same domain name. Adding a vlan to a switch will result the creation of the same vlan in other switches which are in the same domain.But in order to get updates we should configure domain and password. Domain is not related any other system like Windows Domain. It is just used in VTP nothing another else. Vlan trunking Protocol have versions. These are 1,2,3 but 3 is compatible with 1,2 and 2 compatible with

Now the vlan info can be exchanged. Vtp info has a version number after a change the SW which make change increments current version number and then disseminate vlan info with new version number. If we add a SW into the domain which have previous vtp database (which holds vlan info and version) and if his version is bigger then the domain, the new sw vlan info override current domain vlan info. To avoid this you should double check the vtp database.The best way is to delete database file which resides on sw disk named vlan.dat.

Server mode: Server mode is given to switches to manage vlans. Server mode add,delete and change vlan info. After the operation the info is disseminated into other switches in the same domain.

Client mode:This mode is like read only mode. This type of switches just get vlan info and then send it other switches. It updates its vlan database according to this info. In VTP version 1and 2 vlan info resides in ram but in version 3 it is saved in to nvram.

Transparent mode: In version 1 updates doesn’t disseminated, but in version 2&3 updates are disseminated. But updates doesn’t used to update vlan database. Transparent switch doesn’t use or modify domains vlan info. Transparent switches can use vlan database in its own and his vlan database doen’t used by other switches. There are extended and private vlan issues but I will not cover them here. In this mode created vlans are stored in running and startup configurations.

Off mode: This mode is like transparent mode, but in this mode vtp updates doesn’t disseminated.

Vtp pakets is advertised by sending packets to reserved multicast address in through trunk links. So there is no advertisement in nontrunk(tagged) links.

These are global info about update packet means all packets own this infos;